Dave wrote:
Bob, these are SCRs, for sure they stop conducting at zero crossing
only. As far as starting to conduct, are you positive that they do it
very abruptly? I thought that it was not the case, but maybe I am
wrong.


If they're conventional SCRs, yes. If they're GTO (gate turn-off) SCRs,
they can be squinched off while conducting.

LLoyd